The invention relates to a disk brake unit for a vehicle wheel. More specifically, the invention relates to a disk brake unit for a vehicle wheel with a hub having a rotational axis and with a brake disk which is slidable in the direction of the rotational axis but solidly connected to the hub both in circumferential and in radial direction, the hub having an external surface including outer dogs and the brake disk having an internal surface including inner dogs adapted to contact the external surface of the hub.
The bearing and disk brake unit of this type is known in the art. The unit has a hub which is provided at least in parts on its external surface with intermeshing surface features. These features form the outer dogs. Two brake disks having an internal surface provided with corresponding intermeshing surface features are provided, said brake disks cooperating with the hub by way of said internal surface in such a manner that every single brake disk can be shifted relative to the hub in the direction of the rotational axis, but cannot be moved relative to the hub in the circumferential or radial direction.
When braking, high temperatures occur on a friction ring of the brake disk, the complete brake disk getting very hot as a result thereof. This means that the internal casing of the brake disk expands, which reduces the contact with the teeth of the external casing of the hub. This might result in a clearance between brake disk and hub in both circumferential and radial direction.
To prevent such a clearance from forming, the bearing and disk brake unit is provided with three relatively strong leaf springs that are offset on the circumference between internal and external surface, said leaf springs providing an elastic biasing force. However, said leaf springs reduce the axial slidability of the brake disk relative to the hub. Furthermore, high demands are placed on the leaf springs, they must resist high thermal loads. The three leaf springs of one hub must be sufficiently harmonized. The leaf springs must keep functioning for a relatively long useful life without appreciably deteriorating. Accordingly, with the prior art devices, the transition between the internal surface of the brake disk and the external casing of the hub has to meet many requirements. Even at high temperatures, the mechanical connection is to remain readily slidable in axial direction but mechanically so solid in circumferential and radial direction under the elastic biasing force that no rattling, clattering or any other kind of play occurs.
In view of the disk brake unit of the type mentioned herein above, it is the object of the invention to develop the brake disk in such a manner that the contact area between internal and external surface is less subject to thermal load and that elastic means may be dispensed with in said area.
In view of the disk brake unit of the type mentioned herein above, the solution to this object consists in providing the brake disk with an outer ring and with an inner ring, the inner ring and the outer ring being non-rotatably linked together. The outer ring having a friction ring. The inner ring having an internal surface with inner dogs for contacting a hub. Further, the brake disk having a means that prevents heat from being transmitted from the friction ring to the internal surface where the means is arranged between the friction ring and the internal surface.
In accordance with the invention, the heat built up on the friction ring of the brake disk is not directly forwarded to the internal surface of the brake disk, means being provided between friction ring and internal surface which greatly restrict the flow of heat toward the internal surface. As a result thereof, the hub and the parts associated thereto are relieved of the thermal load. The cooperation between internal surface and external surface is simplified and the accuracy of the engagement between the two surfaces improved. Elastic means may be dispensed with here. Thus, the gliding of the brake disks relative to the hub is not additionally hindered either.
The inner ring is also termed a sliding ring. Its function is to cooperate with the hub. It is designed to cooperate with the hub with the least possible play in circumferential and radial direction but to be readily slidable in axial direction. The outer ring is substantially formed by a friction ring. It is suitably connected to the inner ring. The means mentioned may hereby be provided in the connection region between inner ring and outer ring, but they may also be realized by the material of the inner ring, by a ceramic material of the inner ring for example.
The outer ring may be made of ceramics. The inner ring may be made from any other material. Since the ring is divided into an inner and an outer ring, it is possible to utilize different materials, each of them meeting the specific demands placed on the ring. This is a very important step in this field of disc brakes.
The invention makes it possible to considerably reduce the transmission of heat from the friction ring to the other parts of the disk brake unit. This reduces the wear altogether. A brake fluid with a lower boiling point may be utilized. The relative movements between different parts, as they are repeatedly caused to occur by thermal expansion and cooling, are reduced.
In a preferred embodiment of the invention, a ring, the inner ring for example, is provided with fingers which extend in radial direction. The other ring, the outer ring for example, has pockets which are radially accessible and into which the fingers engage. Movement between fingers and pockets is only possible in radial direction. Since the fingers and pockets mesh together, movement in circumferential and axial direction is not possible. But few fingers, and accordingly few pockets are needed to provide a sufficiently dimensioned mechanical connection between inner and outer ring. As a result thereof, the contact between inner and outer ring is reduced to very few contact surfaces. This again means that the transmission of heat from the outer ring to the inner ring is greatly restricted.
In another embodiment, the inner ring is made of a metal with a very low thermal conductivity, more specifically ceramics. The inner ring must not meet the mechanical requirements of a friction ring, it only needs to be sufficiently linked thereto and to be capable of being moved in axial direction. Inasmuch, the ceramics suited for the inner ring are different from those for the outer ring for example. It is also possible to have the outer ring made of ceramics and to utilize its low thermal conductivity, in which case the inner ring is then made of metal or another ceramic material.
In another preferred embodiment, the outer ring is connected to the inner ring in a connecting region in such a manner that the outer ring and the inner ring are capable of being moved toward each other in radial direction. Within the scope of thermal expansion, the outer ring can move radially away from the inner ring. However, movement between outer and inner ring is not possible in axial nor in circumferential direction. In addition to the thermal disconnection, relative movement between outer and inner ring is made possible in this way, said movement taking into consideration the expansion with temperature of the outer ring. The connection between outer ring and inner ring is devised in such a manner that the radial expansion with temperature is made possible. An example of a construction has already been given herein above, the intermeshing of fingers and pockets not only providing a thermal disconnection but also permitting radial movement.
In another preferred embodiment, at least two brake disks are provided and the hub consists of at least two hub portions. Each brake disk is allocated one hub portion. The hub portions are solidly connected to form one whole hub. The division into hub portions facilitates the manufacturing of the hub. The hub portions can be made by stamping for example, which is not so easy to carry out for the hub as a whole.
The internal surface and the mating external surface preferably are given a shape that can be obtained in one lathing step, which makes precision work between the two parts possible. Lathe works of this type are described in EP 97 346 B for example.
In a development, the disk brake unit is inserted into a bearing and disk brake unit. Said unit has a drag bearing which is fastened by means of at least an upper and a lower holding device. The drag bearing constitutes a one-piece cylinder of a cylinder and piston unit. This saves the steps of manufacturing and mounting. Additionally, and irrespective of a subsequent assembly, the axis of the cylinder is parallel to the rotational axis, the accuracy is merely determined by the accuracy with which the drag bearing has been manufactured.
In another improvement, the bearing and disk brake unit has brake pads which are arranged on either side of the at least one friction ring. The brake pads are actuated by the piston of the piston and cylinder unit. The brake pads have guide means for the holding and guiding thereof. They are arranged parallel to the rotational axis and slidable along guide ways. Said guide ways are formed on a guide arm that is configured integral with the drag bearing. It projects in the direction of the rotational axis of the drag bearing and extends over at least one brake disk which it covers on the outside. Brake pads are slidably retained on its guide ways.
The one-piece connection of the guide arm with the remaining drag bearing permits to simplify manufacturing and assembly, the parallel orientation of the guide ways relative to the cylinder""s axis and to the rotational axis is improved, the reaction forces of braking are better directed into the drag bearing. Maintenance is also facilitated. Worn brake pads are more easily replaced and new ones easier to attach.
In another improvement an end piece, which is detachably attached to the free end of the guide arm, only needs to be unscrewed for performing assembly steps on the brake pads. Said end piece is located directly within the force path of the piston of the cylinder and piston unit. It transmits the reaction forces of braking onto the guide arm.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.